Researchers have determined that a specimen of amber from Myanmar originally thought to contain a snail shell in fact contains the juvenile shell of an ammonite, a long-extinct group of cephalopods related to squid and octopuses.
In their paper in the Proceedings of the National Academy of Sciences, "An ammonite trapped in Burmese amber," the researchers use the shell's similarity to a previously known ammonite -- Puzosia (Bhimaites) Matsumoto -- to date the amber as older than the volcanoclastic matrix it was found in, to somewhere within the Albian and Cenomanian ages of the Cretaceous, or around 100 million years ago.
Amber is of course a fossilized form of tree resin which can trap objects and organisms, preserving them (more or less) for millions of years. So how did the shell of an ammonite -- supposedly a strictly aquatic organism -- get trapped in tree resin? The researchers propose three methods:
- Resin from a coastal araucarian conifer dripped down, picking up terrestrial arthropods along the way, before plopping onto an empty ammonite shell that had washed up onto the beach below.
- A tsunami flooded the forest, washing marine debris inland.
- A tropical storm blew the shell inland.
However, they've overlooked two other options: first, and least interesting, a bird might have carried it there (I live within a few miles of the Puget Sound and I've found clam shells on the roof of my house, so this is not unusual); second, and most intriguing, it might be the shell of a tree ammonite!